This invention relates generally to automotive engine controls, and more particularly to a method for estimating the temperature of an exhaust gas recirculation (EGR) valve coil and related apparatus.
Exhaust gas recirculation (EGR) is a process in automotive engines that allows a controlled amount of oxygen-depleted exhaust gas to be mixed with inlet air flowing into an engine for combustion in the cylinders of the engine. Electrically actuated EGR valves are used to control the amount of exhaust gas that is re-introduced into the engine. The EGR valve position is controlled by driving a coil in the EGR valve appropriately. As the temperature of the engine changes, the temperature and electrical properties of the EGR valve coil also change. In order to properly drive the EGR valve coil to attain the desired displacement, it is important to periodically determine the temperature of the EGR valve coil and use this temperature to modify the electrical signal used to drive it.
One known technique of compensating for changes in the EGR valve coil temperature opens the EGR valve during engine idle, a period in which the EGR valve is normally closed. However this method is intrusive and can impact emissions. This method also can impact the quality of the idle operation of the vehicle.
In order to avoid these problems, it is possible to use certain windowing criteria to avoid detection by the driver. However, these windowing criteria can also cause problems, and in some vehicles cause the compensation estimation to fail to update the coil temperature. The result is not only rough idling but also poor emissions performance.
What is needed then is a non-intrusive apparatus for updating the EGR valve temperature that does not cause a rough idle condition and does not worsen emissions. Such an apparatus and related method are provided by the present invention, whose features and advantages will be more clearly understood from the following detailed description taken in conjunction with accompanying drawings.
In accordance with an embodiment of the present invention, the temperature of an EGR valve coil is estimated using only inputs from existing sensors and a model of the relationship between those sensors and EGR valve temperature. This temperature estimation enables continuous prediction of coil temperature under all operating conditions, improving the control of exhaust gas recirculation. The technique improves the vehicle fuel economy and emission performance. Since the technique is non-intrusive, it does not affect emissions and does not impact drivability by creating rough idles. It employs existing sensors to predict the coil temperature, eliminating the need for separate sensors. In addition, the model of this technique is easier to calibrate than other known temperature estimation techniques.
In one embodiment, the temperature is estimated by receiving a charge temperature estimate, an engine inlet air temperature, and a coolant temperature and forming a steady-state EGR valve coil temperature estimate as a linear function of the charge temperature estimate, the engine inlet air temperature, and the coolant temperature.
Such a temperature estimate may be accomplished by an apparatus including first, second, and third multiplication elements and a summing device. The first multiplication element has an input for receiving a charge temperature estimate, and an output, and has a first coefficient associated therewith. The second multiplication element has an input for receiving an engine inlet air temperature, and an output, and has a second coefficient associated therewith. The third multiplication element has an input for receiving a coolant temperature, and an output, and has a third coefficient associated therewith. The summing device has a first input coupled to the output of said first multiplication element, a second input coupled to the output of said second multiplication element, a third input coupled to the output of said third multiplication element, and an output for providing a steady-state EGR valve coil temperature estimate.